Rotary drilling rigs are utilized for drilling a vertical shaft in the earth in search of minerals, water or petroleum products located beneath the surface. The typical rotary drilling rig is a self-contained drilling apparatus which may be transported to the job site. A rotary drilling rig has an upright vertical mast section, a rotary drive unit located at the top of the mast, and means for raising and lowering the drill steel into the drill hole. The drill steel is hollow and the drill bit includes nozzle openings to allow air to be directed through the drill steel to force drilling fines up and out of the drill hole.
An idler guide is located at the base of the rotary drilling rig where the drill steel passes through the bottom mast plate. The guide stabilizes the string of drill steel between the top drive and the drill bit during the drilling operation. The drill steel is subject to wear from the friction produced between the drill steel and the inside of the idler guide as well as the sandblasting effect from the drilling fines blown upwardly and out through the drill hole. The drilling fines may cause increased wear by lodging between the drill steel and the inside of the idler guide. In addition, the entire length of the drill steel in the drill hole is subjected to the sanding effect from the chips and drilling fines blown out of the hole. Since the velocity of the drilling fines decrease as they travel upward through the drill hole, the pipe is caused to wear unevenly. The drill steel outside diameter tapers with the greatest wear occurring on the drill steel located closest to the drill bit. The unevenly worn drill steel and idler guide must be replaced in order for the idler guide to function properly to stabilize the drill steel, reduce noise and reduce the frictional forces on the pipe passing through the bottom of the drill mast.
The typical prior art idler guide has an inner cylindrical sleeve supported for rotation within an outer cylindrical sleeve. Ball bearings are fitted in grooves between the two cylindrical sleeves. The inner sleeve has a central bore through which the drill steel passes. The typical idler guide does not provide any bearing surface for the axial movement of the drill steel pipe, and there is no means for adjusting unevenly worn drill pipe. In prior art idler guides, drilling fines may lodge between the inside diameter of the idler guide and the outside diameter of the drill pipe.
A need has thus arisen for an improved idler guide for reducing the frictional wear from movement of the drill pipe within the idler guide, stabilizing and guiding both new and unevenly worn or tapered drill pipe, and reducing the frictional wear caused by drilling fines lodging between the idler guide and drill pipe.